Crude oil produced from geological formations can contain various amounts of water. Water and crude oil are naturally non-miscible; however, when naturally occurring interfacial active compounds are present, these compounds can aggregate on the water and oil interface and cause water to form droplets within the bulk oil phase. During crude oil lifting through production tubings, the water and oil encounters an increased mixing energy from rapid flow through chokes and bends. This additional mixing energy can emulsify the water and oil. Such an oil external, water internal two-phase system is commonly referred to as a crude oil emulsion, which can be quite stable. The presence of water in crude oil, however, can interfere with refining operations, induce corrosion, increase heat capacity, and result in reduced handling capacity of pipelines and refining equipment. Therefore, the crude oil that is to be shipped out of the oilfield should be practically free of water and usually has a maximum water content limit of about 0.5 to 3% by total weight, depending on the type of crude and oil company.
The emulsified water can also contain various amounts of salts. These salts are detrimental to crude oil refining processes due to potential corrosion in the refinery. In crude oil refining, desalting techniques comprise the deliberate mixing of the incoming crude oil with a fresh “wash water” to extract the water soluble salts and hydrophilic solids from the crude oil. Primary dehydration of the crude oil occurs in oil field water oil separation systems such as “free water knock out” and “phase separators.” Quite often, these systems are not adequate for efficient separation due to factors such as over production, unexpected production changes, and system underdesigns. In these cases, emulsion-breaking chemicals are added to the production processes to assist and promote rapid water oil separations.
Commonly used emulsion-breaking chemicals or demulsifiers include alkylphenol formaldehyde resin alkoxylates (AFRA), polyalkylene glycols (PAG), organic sulfonates, and the like. These compounds, however, may not provide satisfactory performance in all instances. In particular, in extremely cold weather (e.g., −40° C. and below) various problems are known. These active ingredients are typically viscous and require a suitable solvent to reduce the viscosity of the demulsifier blend. Accordingly, there is an ongoing need for new, economical and effective chemicals and processes for resolving emulsions into the component parts of water and oil or brine, including processes and compositions that are suitable for cold climates.
Organic acids are commonly used in demulsifier formulations to enhance performance. Organic acids (and occasionally inorganic acids) are also sometimes used as separate or supplementary treatments to conventional demulsifier formulations. Such acids or formulations containing acids require solvents to stabilize the blend, especially in cold climate conditions where freezing is an issue and pour points of less than −40° C. are required. Inactive solvents comprise large proportions of the total volume of a demulsifier blend, especially when the blend is used in cold climates. The purpose of such solvent is primarily viscosity reduction to allow handling and prevent freezing. The problem is that such blends contain significant amounts of solvent.
A main challenge in oilfield production is the resolution of crude oil emulsions. The emulsions may be water-in-oil, oil-in-water, or complex or multiple emulsions (e.g., water-in-oil-in-water). A reverse emulsion breaker is typically used to treat water external emulsions and a standard emulsion breaker is normally used to treat oil external emulsions. Many reverse emulsion breakers also have a small window of treatment dosages, which makes it challenging and difficult to properly control resolution. Complex or multiple emulsions typically require both a reverse and a standard emulsion breaker to aid in its resolution into clean water and dry oil. These two products traditionally are incompatible, so each must by injected separately. Chemicals that resolve oil-in-water emulsions generally stabilize water-in-oil emulsion and vice-versa. Furthermore, complex emulsions are often produced in oilfields that use steam as a means of enhancing production, particularly in the steam-assisted gravity drainage process.
For this reason it is desired to have a demulsifier that is able to resolve complex or multiple emulsions in a single product application without the need for a two product resolution process. It is also desired to have a demulsifier composition capable of resolving water external and complex emulsions while having a broad dosage range.